In motor vehicles that are (also) driven with an electric motor, such as for example electric and hybrid vehicles, rechargeable storage devices are predominantly used to supply electric power to electric traction motors provided in the vehicle based on the current technology, which are generally referred to as batteries. On known example of these batteries is represented by lithium-ion batteries.
Different technical solutions are in principle available for the charging of the batteries, in particular for wired and inductive power transmission (contactless, free of cables).
The wired power transmission has disadvantages because handling of electric cables is required, while another problem is the compatibility of plugs and sockets, as well as the potential deterioration of contacts when plugging and unplugging of the electric cable is frequently required.
With inductive charging of a battery (often referred to as Wireless Power Transfer or “WPT”), the transfer of energy is carried out with the aid of an alternating magnetic field which is generated in the primary conductor on the side of the infrastructure (primary coil, for example ground coil). A voltage that is induced (electromagnetic induction) with this alternating magnetic field in a secondary conductor (secondary coil) is used in order to charge the battery (so-called “transformer principle”).
To the extent that the terms “primary conductor” or “secondary conductor” are used in this application and in reference to the present invention, these terms are intended in each cases to include also the design or the embodiment of a “primary coil” or a “secondary coil”, or of “primary coils” or “secondary coils”.
When inductive charging is used to charge a battery of a motor vehicle that can be (also) driven with an electric motor, this is particularly useful for a driver because the handling of an electric cable is no longer necessary. It can be also provided that the charging occurs automatically as soon as the motor vehicle is parked at a charging space that is provided with an inductive charging device. Therefore, even comparatively short stops of the driver can be used for at least a partial charging of the battery.
The advantages of inductive energy transfer mentioned above must in particular respect requirement for safety and they must be also compatible with electromagnetic (environmental) requirements. In addition, so that inductive charging of a battery could be carried out efficiently, the primary conductor and the secondary conductor must be overlapping and they should be placed so that the distance maintained between the primary conductor and the secondary conductor is as small as possible. In particular, the size of the air gap between the primary conductor and the secondary conductor of vehicles that are (also) driven with an electric motor, which is often used for charging of batteries, may not exceed a predetermined maximum distance (a desirable distance is 1.0 to 2.0 cm).
Therefore, it is known that especially with so called ground-based charging devices, in which the primary conductor is arranged in a housing that is located in/on the ground, a motor vehicle provided with a secondary conductor (for example an electric vehicle) can be controlled with radio signals, or controlled by the driver in such a way that a very accurate overlapping of the primary and secondary conductor can be achieved. Furthermore, systems that are provided with at least one sensor element are also known, in which for example an optically functioning sensor, such as a laser, Lidar or a scanner system are built to detect a path through which an electric motor vehicle can be guided to a charging station.
Moreover, to provide an optimal distance and compensation that will be as complete as possible for a given offset between a primary and secondary conductor can be achieved for example when, after a motor vehicle makes a stop at a charging station, the primary conductor is moved in the direction of the secondary coil, or the secondary coil is moved in the direction of the primary coil, wherein a movement of the respective coil can be made in one, two or all three spatial directions.
However, with a large number of ground-based charging stations for electric vehicles, for example at the side of the road and in parking car parks, the problem is that sufficient protection of the ground-based charging stations has not been achieved yet. That is why in ground-based charging stations, but also in other charging stations for an inductive transmission of electric energy in which the primary conductor or a housing with the primary conductor can be moved to achieve the goals mentioned above, the problem is that at temperatures around and below the freezing point, freezing of the primary conductor or of the housing which contains the conductor, which can become frozen to the surrounding ground or floor, to the road surface, or to other devices surrounding the housing of the primary conductor, etc., can occur, which means that it is then not possible to move the primary conductor.
From DE 24 34 890 B1 is known an inductive charging device in which a transformer part that is associated with a parking space is provided with structural elements in the form of heating spirals generating electric loss with heat so as to keep ice off the dome surface of a charging plank in winter.
Also, DE 10 2011 076 186 A1 describes an arrangement for providing a remedy during a fault of a wireless energy transfer with a first component, which may be for example mounted on a roadway and which is provided with a fault recovery means, wherein the fault recovery means may be provided in addition to an existing coil for the induction with a heating element for melting ice or snow, or for drying the first component.